The invention addresses cutting tools used to remove material such as from a workpiece or bulk feedstock. More specifically, it addresses such tools that employ a round cutting insert that rotates under the force of the material removal process as a result of the cutting insert being affixed to a support device that permits rotation about the axis of the cutting insert. The most basic representation of a round cutting insert 1 is depicted in FIG. 1a; it is fundamentally a disk having an axisymmetric peripheral surface 2, two axisymmetric end surfaces 3, and insert axis 4 about which said surfaces are axisymmetric. One or both the end surfaces 3 can be partially or entirely non-planar and the peripheral surface 2 may also be non-cylindrical, one example of which is shown in FIG. 1b. There are two basic configurations for machining with a round cutting insert. A conventional radial mount is shown in FIG. 2 (a face milling tool as an example) where flank surface 5 is the peripheral surface 2 and rake surface 6, the surface on which the chip of removed material is formed, is one of the end surfaces 3. This type of configuration is the subject of numerous patents, such as U.S. Pat. Nos. 2,885,766A, 3,329,065, 4,477,211, 5,478,175. The other configuration is a tangential mount as shown in FIG. 3 (a face milling tool as an example) where rake surface 6 is the peripheral surface 2 and flank surface 5 is one of the end surfaces 3. This type of configuration is the subject of numerous patents, such as U.S. Pat. Nos. 2,127,523, 2,233,724, 2,551,167 and 4,223,580 for single-point lathe processes used to create surfaces of revolution and more recently U.S. application Ser. No. 14/502,035 for a variety of multi-tooth processes where compactness of the rotary support device upon which the round cutting insert is affixed is important, as compared to many lathe applications. In all cases, the circular intersection of flank surface 5 and rake surface 6 defines a round cutting edge 7. Generally, for a rotating round cutting insert, there must be a central hole 8 to facilitate mounting cutting insert 1 to rotary support device 21.
When machining, heat energy is generated by friction and deformation of the workpiece material (i.e., the cutting process) that is then imparted from the cutting process into the cutting insert. As the rate of heat generation in the process increases, such as by running the cutting tool at a higher cutting speed, the temperature of the tool (i.e., the cutting insert) increases. Increased temperature is a primary cause of increased tool wear rate. Allowing the cutting insert to rotate helps to moderate the effect of heat energy generated by the cutting process, extending tool life and/or allowing the cutting tool to operate at higher speed without excessively compromising tool life. Rotation of the cutting insert without human intervention also allows the entire circumference of the round cutting insert, the round cutting edge, to be fully consumed with no need for human intervention to rotate to fresh regions of the circumference (referred to as indexing), which is required for non-rotating cutting inserts.
The need for a rotary support device that constrains five degrees of freedom while allowing one degree of freedom to be free, that is, the noted rotation about the axis of the round cutting insert, adds manufacturing cost to the cutting tool. Keeping manufactured cost low enough so that the increased performance of a rotating-insert cutting tool is sufficient to justify its added purchasing expense has been a consistent challenge in previous attempts at commercializing such cutting tools. A main driver of this challenge is the extreme operational demands on the rotary support device, the cutting insert, and the cutting insert's connection to and interface with the rotary support device. The present invention addresses the numerous past shortcomings in meeting the operational demands in a manner that is geometrically compact and cost effective.
One of the main challenges is that the rotary support device, and the cutting insert itself, must mechanically support the high cutting process forces. For the cutting insert, ample cross-section is required so that it does not crack, and a larger cross-section consumes more of the limited space available. For the rotary support device, the challenge lies in transmitting/supporting the noted forces across its internal surfaces that allow relative rotary motion to occur while constraining all other motions, and at the same time maintaining sufficient cross-sections to avoid cracking or other deformation failure, again, all this being achieved in the limited space available.
Relative rotary motion is provided by “bearings”. In plain bearings static friction between two mating bearing surfaces is overcome to allow relative motion due to sliding. In rolling-element bearings relative motion occurs due to rolling of round elements (e.g., balls/spheres, cylinders, or frusto-conical (tapered) solids/rollers) between the two bearing surfaces. Commercial-off-the-shelf rolling-element bearings incorporate the bearing surfaces into components referred to as “raceways” or races, for short. For rolling-element bearings there is minimal (in some cases theoretically zero) sliding friction. The rotating-insert cutting tool application requires extremely compact packaging of the bearings relative to commercial standard bearings that would be specified to support forces of the magnitude seen from the cutting process. Thus, to summarize, one of the longstanding challenges that have inhibited the widespread practical commercial adoption of rotating-insert cutting tools is the need to arrange and package the bearings very compactly while being able to support the high forces without catastrophic failure or a limited fatigue life. Commercial-off-the-shelf rolling-element bearings generally do not exist to such optimal levels of load bearing capacity, in the needed degrees of freedom, relative to the size of the bearing; that is, there is not sufficient market to motivate bearing companies to design and produce such size-optimized bearings, at least not for most metal-cutting applications where it is preferred or required that the cutting insert be small (for example and without limitation, less than 25-30 mm in diameter). For example, in U.S. Pat. No. 4,477,211 for a “rotary tool cutting cartridge”, the rotary support device (the rotary tool cutting cartridge) employs lower and upper rolling-element thrust bearings and radial needle-roller bearings that make use of a specially designed housing as the bearing raceways and in such a way as to maximize the number of rolling elements. Still, while space is saved by not using a pre-packaged off-the-shelf bearing and rather using a special-purpose housing, that housing exhibits significant bulk in its cross-section.
Another significant shortcoming in past attempts at commercial application of rotating-insert cutting tools is contamination of the bearing surfaces noted above. Particles of removed material, dust, and even metal working fluid, that infiltrate from the working environment into the bearings can have a deleterious or even catastrophic (seizing the relative motion) effect. In general applications where relative rotary motion occurs between plain and/or rolling-element bearings, the bearing surfaces are packaged in such a way as to seal out external contamination. Rotary seals that are very compact are difficult to find with the exception of those that are built into standard bearings that, as noted, generally do not meet the size/packaging needs of this application. Thus, a specially designed rotary support device requires the use of either standard seals or specially designed seals. The former are available, like bearings, in general purpose designs that are not as compact as desired, and the latter are either very expensive or, in at least some known examples, result in excessive friction, wear and reduction in sealing performance over time. For example, U.S. Pat. No. 4,477,211 employs an O-ring to seal the lower end of the rotary support device (referred to as a “cartridge” in the reference) or, as an alternative, a C-ring. The product based on this patent and sold by Rotary Technologies Corp. ultimately employed a C-ring seal that consumes 1.4 mm radially and 2.5 mm axially. A second-generation product offered by Rotary Technologies Corp., based on U.S. application Ser. No. 12/350,181, actually does use an O-ring, as called out in that application. While it seals well, and is more compact (0.9 mm radially and 1.0 mm axially), it is extremely tight causing significant friction. In fact, the O-ring approach to a rotary seal, while elegant and simple, is not a usual use of an O-ring, and is not well suited due to the typical tolerances on the cross-sectional size of the O-ring section. As a result, accommodating the noted tolerance requires the seal to be excessively tight/compressed at one end of the tolerance band. It then wears significantly and eventually may lose its sealing ability due to wear.
Along with the challenge noted to support the cutting process forces by the rotary support device is the consideration of what it means to “support” the forces. Metal-cutting (and when cutting materials other than metal in order to produce a new surface intended ultimately for some function) requires the support of those forces to be stiff enough that the deflection of the cutting insert relative to the workpiece (tool-work deflection) is small enough to provide acceptable results. First, the rigidity must be sufficient to avoid unstable vibrations in the noted tool-work deflection, referred to as chatter. Second, the rigidity must be sufficient to avoid tool-work deflection large enough that the dimension and/or surface finish of the machined surface feature do not meet the specified tolerances, which in many cases are fairly tight. For past implementations of rotating-insert cutting tools, maintaining precision of the produced surface has been a challenge due to the need to maintain a relatively rigid support of the cutting insert in five degrees of freedom (three translational, two rotational) while allowing it to also freely move in the sixth degree of freedom (rotation about the axis of the round cutting insert). The bearing arrangement noted in U.S. Pat. No. 4,477,211, where radial bearings are used along with axial thrust bearings, is common across known attempts at applying rotating-insert cutting tools. While it is routinely possible to apply an axial preload to eliminate axial clearance/slop in the rotary support device, that is not possible in the radial direction when using a radial bearing. This is critical in that the cutting insert is then not completely constrained in all the degrees of freedom other than that of the cutting insert axis of rotation. The result is a compromised finish/roughness on the surface produced; often there are small serrations or waves that fully (six-degree-of-freedom) constrained cutting inserts do not produce. No realistic tolerance on the diametric surfaces between which radial rolling elements are located can eliminate the noted radial clearance/slop.
Also posing a challenge in regard to precision in the machined surface is how well the round cutting insert is centered/concentric about the rotary axis of the rotary support device. This is largely influenced by the means of how the cutting insert is located on the rotating portion of the rotary support device (in the configurations considered here, that is referred to as the “rotor” as it rotates relative to the fixed “stator”, and the cutting insert is affixed to and located by the rotor). Many past attempts at commercial rotating-insert cutting tools require an inner diameter of the cutting insert to match the outer diameter of a mating element, such as the rotor, in close slip-fit tolerance while that inner diameter of the cutting insert must also exhibit a close/tight concentricity tolerance relative to the round cutting edge. Of course, this all also presupposes that the inner bearing surface of the rotor is closely concentric to its outer diametric surface to which the insert is located by its inner diametric surface, and that there is minimal radial clearance/gapping between the needle rollers and the rotor inner diametric surface and the supporting diametric surface of the stator. All these noted requirements for close tolerances and concentricities add cost to the rotary support device itself and the cutting insert, and for the usual radial bearing no practical tolerance can eliminate the radial bearing clearance/gapping/slop noted above. As noted, one of the main commercial challenges in rotating-insert cutting tools is their high cost, both in the cutting tool (rotary support device) itself and in the disposable/perishable cutting inserts.
Another less quantifiable challenge to successfully meeting the needs of a commercial market with rotating-insert cutting tools is their ease of use. Compared to traditional fixed (i.e., non-rotating/nonmoving) cutting inserts (relative to the cutting tool body to which they are attached) rotating-insert cutting tools have inherent complexity. Furthermore, due to the inherent potential for rotation of the cutting insert relative to the rotor, provisions must exist that eliminate the potential for the cutting insert to become loose or disconnected from the rotor, such as by loosening of a threaded fastener due to induced rotation of the cutting insert relative to the rotor that, through friction between the cutting insert and a mating threaded fastener that is threaded onto/into the rotor, causes the threaded fastener to loosen relative to the rotor. One solution is to use a left-handed fastener to affix a rotating insert that rotates in a left-handed fashion (and right-handed, vice versa) so the potential insert-rotor relative rotation would serve to tighten the fastener. This requires that a left-hand version and a right-hand version of the rotary support device be made available to customers to serve all types of cutting tool needs. This is the approach taken in the products of Rotary Technologies Corp. based on U.S. Pat. No. 4,477,211.
Another approach is to have one or more threaded fasteners that hold the cutting insert to the rotor in ways that avoid the axis of the threaded fasteners being coaxial with the rotor-insert axis. One manner of taking this approach was indicated in U.S. patent application Ser. No. 12/350,181. In most cases due to size/compactness limitations, this involves small screws and small tools. In the product line that resulted from that patent application, to avoid the small screws and tools, a cutting insert retention device was devised (not in application Ser. No. 12/350,181) that tightens to itself and, in so doing, cinches onto mating geometry on the rotor to clamp the cutting insert against the opposing axially planar mounting surface. As such, any relative rotation between the cutting insert and rotor cannot loosen the insert retention device since its threaded tightening happens between two components within the retention device. In the example noted, the insert retention device may work quite well, but it is not familiar to most users, requires special tools, and is of high cost and complexity.
Finally, coming back to cost as an ultimate practical commercial hurdle, a general challenge to any design of such a system is the recognition that all the noted challenges must be overcome with special designs that are economically produced/manufactured at the production volumes that are generally low relative to commercial, general-purpose bearings and seals, for instance. The present invention takes into consideration these production volume cost drivers as well.
The domain of application includes various types of cutting tools used to produce various types of surfaces in various types of work materials. A round cutting insert mounted to a rotary support device may be attached to a cutter body that is rotated at high speed on a machine spindle to perform operations such as, but without limitation, face milling, end milling, drilling, or cylinder boring. The round cutting insert mounted to a rotary support device may also be attached to a shank that is affixed to a lathe to perform OD turning, ID turning/boring or facing. The cutting insert may be oriented relative to the cutting motion in either a conventional radial mounting or a tangential mounting, as noted earlier. In many cases, the “rotary support device” may be termed a rotary “cartridge” or “cassette”; it is affixed to the cutter body, upon which is affixed a cutting insert, to comprise the cutting tool. For cutting tools like face mills and cylinder boring tools that employ more than one cutting insert, it is often important that at least one cutting insert be precisely positioned in the depth-of cut direction relative to other cutting inserts. For this reason, this invention provides an embodiment that incorporates adjustability to the rotary support device, which from this point forward may be abbreviated RSD.